This invention relates to improved operation of turbochargers as applied to internal combustion engines and the like. The general concept of turbo-charging is to employ the residual energy in engine exhaust to increase induction air pressure before final compression in the engine. It is internal combustion engines with which this invention is particularly concerned, of any combustion cycle, and preferably those state of the art engines into which fuel is fed according to regulatory environmental factors to which said engines are subjected; all of which includes the type of fuel, the mode of feeding said fuel, the angular velocity and torque change or constants, and the various temperature conditions, all as circumstances require. And in view of efficiency and environmental regulatory requirements, it is a general object of this invention to provide substantially instantaneous increases in induction air pressures into the engine according to variations in performance demand. To this end, the compressor rotor of the turbo-charger can be accelerated independently of the turbine rotor thereof, whereby the mass inertia of the turbine rotor does not retard acceleration of the compressor rotor.
Internal combustion engines are characterized by two basic requirements, controlled fuel feed, and the proper induction of air to establish a correct air-fuel ratio required for efficient combustion. These two basic requirements are interrelated and are subject to electronic computer control. State of the art electronics provides instantaneous operational calculations to which the engine must respond in order to achieve efficient operation with any internal combustion engine having multi-port, throttle-body or direct injection irrespective of fuel type. However, despite the instantaneous demand for increased combustion air due to sudden changes in load and torque demand, there is an inherent "turbo-lag" involved in the acceleration of state of the art turbochargers. In the internal combustion engine, carburetor fuel feed has been greatly replaced by electronically controlled fuel injection, the amount of fuel injected being determined by the time during which the injector remains in the "ON" position, calculated by an electronic computer geared to various parameters including; absolute pressure in the inlet manifold, Air flow rate, RPM, engine load, crankshaft position related to T.D.C., engine coolant temperature, engine inlet air temperature, exhaust oxygen content, and torque demand. Also, internal combustion engines are often supercharged with induction air and subject to wide ranges of operational requirements under varying conditions. And, heretofore the prevailing deficiency has been "turbo-lag" in the induction air pressure supplied, this time-lag resulting in deficient engine operation. It is therefore an object of this invention to provide a method and apparatus by which adequate combustion air is substantially instantaneously supplied to the induction manifold of an internal combustion engine.
The method and apparatus herein disclosed gives increased power and makes the engine more flexible and more responsive, for any given engine RPM and/or torque requirement. Cold starting becomes improved allowing immediate augmentation of engine compression heated air flow, and all adjustments become automatic. It moreover simplifies the fuel control process which enhances compliance with exhaust emission regulations, being a rational method and/or system which allows the engine to be fed adequate induction air as necessary together with adequate fuel for proper and efficient operation under all conditions of use.
State of the art turbochargers employ a "unitized" principle of construction, wherein the compressor rotor and turbine rotor are integrally coupled by a common shaft. Therefore, the mass of each is combined with the other so as to affect common acceleration and deceleration. It is the acceleration of the compressor rotor with which this invention is particularly concerned, because the turbine rotor is inherently coupled to respond to exhaust gas energy discharged from the engine combustion chambers. Furthermore, said exhaust gases are not increased (or decreased) in pressure and/or velocity until after a change in induction pressure and combustion temperature occurs. Accordingly, there is a measurable time period before an exhaust pressure change reaches the turbine rotor, and only then does the turbine rotor respond to gradually increase its momentum, while the engine waits for the required induction pressure increase to be reached. The result is "turbo-lag" during which the engine is starved of adequate induction air for proper acceleration.
The state of the art provides auxiliary prime movers for supplementing the turbine drive in order to accelerate the mass of the combined rotor components. However, there are at least two problems here. 1) The mass of the two rotors is approximately twice that of either, and rapid acceleration of the compressor rotor is essential in order to enhance air induction. Heretofore, the torque required of the auxiliary prime mover has been twice that which would be required to accelerate the compressor rotor alone, and therefore it is an object of the invention to disengage the compressor rotor from the turbine rotor and thereby maximize acceleration of the former independently of the latter. In practice, this separation occurs during the initial phase of acceleration, as will be apparent from the following: 2) The auxiliary prime mover is preferably an electric motor having high initial torque and acceleration. However, state of the art electric motors have RPM limitations which are exceeded by the ultimate RPM attained by state of the art turbochargers here under consideration, and therefore it is an object of this invention to isolate the RPM restricted electric motor drive from the ultimately higher RPM drive of the turbine rotor and compressor rotor when driven thereby. This arrangement thereby provides a substantially instantaneous supply of adequate induction air pressure to be followed by a "take-over" effect as and when the turbine rotor drive exceeds the "limit RPM" range of the motor drive.
From the foregoing it will be observed that there is a primary objective to protect the auxiliary electric motor drive from exceeding its structurally limited RPM which is lesser than turbocharger RPM. Heretofore, "single direction bearings" have been employed in the art in order to couple the prime mover auxiliary to the unitized compressor rotor and turbine rotors. It is therefore an object of this invention to provide a coupling means that transmits torque applied by said auxiliary electric motor drive to the compressor rotor. In practice, this is achieved by utilizing a hysteresis or eddy-current coupling that transmits torque to the compressor rotor during an "acceleration mode", and which relinquishes its drive effect as and when the limit RPM of said motor is reached, whereupon the turbine rotor continues to accelerate the compressor rotor into a "running mode" beyond the auxiliary motor limit RPM.
It is also a primary object of this invention to separate the mass to be accelerated, and to reduce torque required of the auxiliary electric motor drive as well. To this end, the compressor rotor is disconnected from the turbine rotor during the acceleration mode, thereby permitting the compressor rotor to overrun the speed of the turbine rotor, which occurs during the acceleration mode when there is an increased induction air pressure demand. In practice, an overrunning clutch is ultilized for this function, whereby the compressor rotor mass is independently accelerated from the detached turbine rotor mass. As a result, the turbine rotor mass is free of the compressor rotor load and independently lags for its maximized acceleration comensurate with the delay in exhaust gas discharge which is reduced from the engine which is waiting for the induction air pressure increase demanded thereby. Accordingly, the compressor rotor mass is accelerated together with the auxiliary electric motor drive therefor, and the turbine rotor mass is accelerated alone by the available exhaust gases.
It is also an object of this invention to combine 1) the aforesaid object to provide a coupling means to transmit torque applied by said auxiliary electric motor drive and 2) the aforesaid object to separate the masses to be accelerated. Accordingly, the ultimate embodiment of this invention is to provide a coupling means that transmits torque to the compressor rotor by the auxiliary electric motor drive to its "limit RPM", and a coupling means for separating the mass of the turbine rotor during the acceleration mode. Accordingly, the compressor rotor is accelerated substantially instantaneously in response to induction air pressure demand in order to supply adequate combustion air for establishing a proper ratio of fuel to air mixture; all of which decreases the time interval required for effecting the process as herein disclosed.
The combination of a turbocharger with an auxiliary electric motor drive involves factors which have not been addressed in the prior art. High RPM is required of the turbine driven compressor, in a range up to 150,000 to 200,000 RPM and more, and this precludes the use of anti-friction ball, needle or roller bearings, with reliance upon sleeve type "hydrodynamic" bearings having substantial play in the form of radial clearance. However, the auxiliary electric motor drive is subject to critical concentricity and must rely upon precision ant-friction bearings such as ball bearings, which have a restrictive "limit RPM" range of 50,000 to 80,000 RPM (less RPM as size and mass increases), in order to achieve practical longevity. It is these two diverse concentricity factors that has resulted in destructive forces when applied to coupling means such as a Sprague overrunning clutch and the like, in which concentricity is critical wherein one clutch member is carried on a precision axis whereas the other clutch member is carried on a non-precision axis. Heretofore, these two diverse axes have been treated as one in fixed alignment of the turbine-compressor shaft with the auxiliary motor drive shaft. The result is destructive radial displacements to the overrunning clutch therebetween such as a Sprague or the like here under consideration. It is the radial play that produces eccentric displacement between said two axes that adversely affects mechanical couplings and clutches. Therefore, it is a primary object of this invention to eliminate the prior art incompatibility of motor and turbine bearing related functions, by separation thereof onto two distinct axes of rotation without adverse affect with respect to coupling means therebetween.
It is the aforesaid coupling means that is replaced in order to provide the aforesaid separation of axes, whereby mechanical contact between the compressor rotor and motor shaft is eliminated. In practice, an eddy-current clutch is provided for this purpose, the air gap of said clutch being non critical and such that the radial displacements experienced with hydrodynamic bearings of turbochargers are tolerated with the absence of direct mechanical engagement. Radial displacement of the hydrodynamic bearings may be as much as 0.005 to 0.008 inch; whereas the concentricity of the precision motor shaft bearings are within 0.0001 to 0.00005 inch (approximately). This is a hysteresis drive commonly referred to as an eddy-current clutch, as it is employed herein to couple the auxiliary electric drive motor to the compressor rotor or unitized compressor-turbine rotors as the case may be. Accordingly, radial play hydrodynamic sleeve bearings are made compatible with precision drive motor bearings, characterized by a distinct separation of rotation upon individual axes.
It is another object of this invention to provide a coupling means in a compressor-turbine unit for disengageably driving the aforesaid compressor rotor from the turbine rotor. In practice, an overrunning clutch is employed for this purpose, preferably a Sprague type clutch in which concentricity of its disengageable members is critical. Accordingly, the compressor-turbine unit axis is journaled on non-precision sleeve type hydrodynamic bearings having radial play, whereas the compressor rotor is journaled on precision anti-friction needle bearings coaxially within the compressor-turbine unit.
It is still another object of this invention to provide means for engaging and disengaging the aforesaid hysteresis drive or eddy-current clutch responsive to inertial reversals of torque between the motor drive and driven compressor rotor or turbine-compressor unit as the case may be. In practice, the eddy-current clutch is comprised of a retractile magnet drive member that slides over a driven magnetic member by means of a helix on the driving motor shaft and a nut on said driven member, as later described. Forward acceleration of the drive motor shifts the drive member over the driven member, whereas reverse deceleration of the driven member relative to the drive member by means of the overtaking turbine driven compressor rotor exceeding the speed of the motor drive thereby retracts the nut and driven member. Accordingly, the eddy-current clutch is functional during the "acceleration mode" and disfunctional during the "running mode", there being a rapid velocity change in rotational speed from low to the "limit RPM" speed and also between the "limit RPM" and subsequent higher speed of the turbine driven compressor.